Overlapped document detector

ABSTRACT

An apparatus and method for detecting overlapped documents in which documents are transported between normally open port means which are connected by means of fluid passageways to a vacuum source. Each port means is a part of a continuous fluid loop circuit which includes a pressure responsive switch means and which is closed to the atmosphere except for the normally open port means. When a document passes between the port means, it is attracted against one or the other of the port means thereby closing that port means, causing the fluid loop of which that port means is a part to become completely closed to the atmosphere, and causing the pressure responsive switch means in that fluid loop to change state. Circuit means are connected to both of the switch means to determine when they are in the changed state simultaneously. Included in the circuit means is circuitry for insuring that the switch means are in the changed state simultaneously for a predetermined minimum period of time before an output indication is produced, thereby eliminating false output indications which may be produced by documents which are wrinkled.

United States Patent 1 Burroughs Nov. 20, 1973 OVERLAPPED DOCUMENT DETECTOR [57] ABSTRACT [75] Inventor: Frank P. Burroughs, Kensington, An apparatus and method for detecting overlapped M documents in which documents are transported between normally open ort means which are connected [73] Asslgnee: OpncalRecogmtlon Systems by means of fluid pa sageways to a vacuum source.

lhcqrpqrated, Resto"! v Each port means is a part of a continuous fluid loop [22] Filed: Jam 11, 1972 circuit which includes a pressure responsive switch means and which is closed to the atmosphere except PP 217,004 for the normally open port means. When a document passes between the port means, it is attracted against 52 Us. (:1. 271/57, 192/128 the thet t means thereby closing [51 Int. Cl B65h 7/12 that means causthg the fluid which that [58] Field of Search 271 /56, 57, 47, 64 MA; P means is a P P Y 610864 192/128, 125 C; 73/37], 375 the atmosphere, and causing the pressure responsive switch means in that fluid loop to change state. Circuit [56] References Cited means are connected to both of the switch means to determine when the are in the chan ed state simulta- UNITED STATES PATENTS neously. Included in the circuit meafis is circuitry for 3,504,9l l 4/1970 sllverberg 271/56 insuring h h it h eans are in the changed State simultaneously for a predetermined minimum period 3:627:303 12 1971 Zeewy .1: 271 57 of befme an output ndcanon Produced thereby eliminating false output indications which may FOREIGN PATENTS OR APPLICATIONS be produced by documents which are wrinkled. 939,269 /1963 Great Britain 73/37.7

Primary ExaminerEvon C. Blunk Assistant Examiner-Bruce H. Stoner, Jr.

Attorney-Francis C. Browne et al.

8 Claims, 2 Drawing Figures +5 VD.C 5 I2 53 9 l9 E E 3 P4 L CLOCK 5 3 7 56 55 Q DOUBLE 5| FEED 29 57 VAC. SOURCE OVERLAPPED DOCUMENT DETECTOR This invention relates to an apparatus and method for detecting the passage of overlapped documents.

In many different kinds of systems, for example document reading systems and bookkeeping systems, it is necessary to pass a series of documents one at a time to a station for processing. It is crucial to the proper operation of these systems that only one document appear at the processing station at any given time. In order to avoid sending two overlapped documents which have become stuck together to the processing station at the same time, a device for detecting the passage of over lapped documents must be provided.

Some overlapped document detectors of the prior art have operated on principles of fluidics. These detectors typically have comprised a vacuum source connected to two passageways each of which terminates in an orifice on one side of an area through which documents are transported. When overlapped or double documents appear between the orifices, one document is attracted to a position covering each orifice by the vacuum pressure generated by the vacuum source. The covering of the orifices, in turn, causes a change in pressure either in the area between the orifices or in the passageways which operates a pressure responsive switch at one of those locations.

One problem associated with the overlapped document detectors of the prior art has been their slow speed of response. Put another way, these systems have been unable to change pressure conditions rapidly enough to respond to the normal rapid passage of documents in a document processing system. Another disadvantage associated with the prior art overlapped document detectors has been the requirement that a relatively high pressure source be used.

The present invention obviates the above problems by providing a low volume, low vacuum overlapped document detector including a novel fluid circuit which uses ultra-sensitive pressure responsive switches. Because the detector of the present invention requires only a small amount of air to be moved for the switches to change state, it is extremely rapid in response and permits a relatively low pressure vacuum source to be used. Use of a low pressure vacuum source besides being more economical, does not result in the documents being retarded by a high vacuum pressure as they pass the ports of the detector.

It is therefore an object of the invention to provide a low volume, low vacuum fluid system to detect the presence of overlapped documents.

It is a further object of the invention to provide an overlapped document detector including a novel fluid circuit using ultra-sensitive pressure responsive switches, which results in an extremely fast speed of response and which permits the use of a relatively low pressure vacuum SOUI'C.

It is still a further object of the invention to eliminate false output indications which may be caused by wrinkled documents.

It is a further object of the invention to eliminate paper dust from interfering with the operation of the pressure responsive switches.

The above objects are accomplished by the present invention by providing two port means directly opposite each other and defining a given area through which the documents to be detected are transported. Each port means is the only open part of a continuous, closed fluid loop circuit which includes a pressure responsive switch means and which is connected to a vacuum source means. Single documents transported through the given area between the port means will due to initial proximity be attracted by the subatmospheric pressure generated by the source means to either one or the other of the port means. Closure of a port means by a document completely closes the fluid loop circuit with which that port means is associated and the change of pressure across the switch means in the fluid loop causes that switch means to change state. When overlapped documents are transported through the given area, both port means are closed by the documents and both of the switch means change state. A coincidence detector is connected to the switch means to indicate that a double document condition is present. To prevent a wrinkled document from causing a false output indication novel circuit means is provided which causes an output indication to be emitted only if the port means are simultaneously closed for a minimum predetermined period of time. The output of the novel circuit means may be connected to a means for automatically stopping the operation of the machine so that the double document condition may be corrected.

The invention is described in greater detail below in connection with the following figures.

FIG. 1 is a schematic diagram of a preferred embodiment of the overlapped document detector of the invention.

FIG. 2 is a schematic diagram of an alternate embodiment of one of the fluid loops of the overlapped document detector of FIG. I.

In FIG. 1 documents are fed from conveyor belts 29 and 37 which are operated by pulleys 33 and 34 to the area between port means 23 and 24 which are located in shoes 25 and 26 respectively. After passing through the area between the port means, the documents are picked up by conveying belts 30 and 38 operated by pulleys 35 and 36 and are transported to the remainder of the processing system, for example to a processing station.

Vacuum pressure is applied to port means 23 and 24 by means of a vacuum source through fluid passageways 2, 3, 5 and 7, and 50, and 2, 4, 6, and 8 and 39 respectively. The vacuum pressure appearing at port means 23 and 24 ideally should be great enough to attract documents of the thickness and stiffness being used but should not be so great so as to substantially retard the movement of the documents through the system. The fluid passageways of the system may be constructed of rubber, plastic, polyethylene, or any other suitable material ordinarily used for the transmission of fluids.

Normally open port means 23 and 24 are the only open parts of the otherwise closed fluid loop circuits comprised of passageways 7, l2, 14, 22, and 8, ll, 13, 21 respectively. Included in these fluid loops are pressure responsive switches 13 and 14 each of which is comprised of a housing in which is located a flexible diaphragm, a movable contact which may be mounted on a leaf spring, and a stationary contact. Switch 13 includes diaphragm 15, movable contact 16 and stationary contact 17 and switch 14 includes diaphragm l8, movable contact 19 and fixed contact 20. When diaphragm l5 and 18 are deflected by a pressure differential across the switch in the proper direction, they displace movable contacts 16 or 19 respectively so that contacts 16 or 19 come into contact with fixed contacts 17 or 20 respectively. The movable contacts may be mounted on leaf spring for movement.

With no documents in the area between the normally open port means vacuum source 1 applies a vacuum pressure through passageways l2 and 11 to diaphragms l and 18 causing them to displace movable contacts 16 and 19 against stationary contacts 17 and 20 thereby rendering pressure responsive switches 14 and be attracted by the vacuum pressure in the area between the port means to either port means 23 or port means 24. it will rest against port means 23 or 24 as it continues its movement through the area between the port means and will thus close the port means.

Let us-assume that a single document has been attracted to port means 24, thereby closing this port means from the atmosphere. Closure of port means 24 1 completely closes the fluid circuit 8, ll, 13, 21, 39, and

because there is no atmospheric air to be pulled by the vacuum source, there is no air flow in the closed loop, and the pressure on both sides of switch 13 becomes equal.

This causes diaphragm to assume its relaxed position thereby allowing movable contact 16 to return to its normally biased position breaking contact between contacts 16 and 17 and operating switch 13 to the open position. If a single document passing through the area between the port means is attracted to port means 23, the same process occurs in fluid circuit 7, 12,14, 22, 50 and switch 14 is operated to the open position.

The rapid switching speed of the overlapped document detector is due in large part to the fact that ultrasensitive pressure responsive switches capable of changing state in the presence of minute pressure differential used in the novel fluid circuit of the invention. A switch found suitable for use in an actual device constructed according to the invention is the PSF 100a Ultra-Low Pressure Sensor manufactured by Fairchild Controls. This switch changes state at a minimum pressure differential of 56 inches H 0 and has a maximum switching speed of 40 c.p.s. The vacuum pressure source used in the actual device constructed produces a vacuum pressure of 9 '12 inches H O.

The outputs of switches 13 and 14 are connected to a coincidence detector. When two documents simultaneously pass through the area between port means 23 and 24, one document is attracted against each port means. Both of the fluid circuits are thereby completely closed from the atmosphere and both switches 13 and 14 are opened simultaneously. The coincidence detector is operative to detect this condition and to provide an output signal in response to it.

in order to avoid a false response due to the fact that a wrinkled document may "look" to the port means as though it were two documents, circuitry is provided which requires that both switches 13 and 14 be opened 4 simultaneously for a predetermined minimum period of time before an output indication is produced.

The port means are made small with respectto the size of the document and, are placed directly. opposite each other so that a wrinkleddocument .cannot .cover both port means at the same time. Due, however, to the fact that switches as a rule are generally not perfect and a switch may stutter after it has changed state and momentarily returned to its initial state before finally assuming the changed state, a wrinkled document may appear to the detector as if it were; two documents. Thus, a wrinkled document may first, for instance, cover port means 24 and open switch means 13. it may then, if it is in a wrinkled condition, cease to cover port means 24 and cover port means 23 whereupon switch 14 will be opened and switch 13 will be closed. Due to stuttering, however, switch 13 may momentarily open before finally assuming a closed state whereupon switches 13 and 14 will be momentarily opened at the same time. The circuitry which is described below is arranged so that it does not provide an output indication unless switches 13 and 14 are simultaneously open for more than a predetermined time which time is greater than the momentary coincidence of the switches due to stuttering and which may be optimally determined for any given system by routine experimentation. in an actual device built according to the invention, the time was set to between 2/9 and 2/5 of the time that it takes a single document to transverse the area between the port means.

Switches 13 and 14 are connected between ground on one side and a S-volt D.C. supply source on the other side through resistors 52 and 53 respectively. The side of each switch which is connected to the resistors is also connected to one input of NAND Gate 51 which provides an output signal at all times except when input signals are simultaneously present at its input. The output of NAND Gate 51 is connected to one input of AND Gate 55, the other input of which is connected to a source of clock pulses present at the output of inverter 54. The output of AND Gate 55 is connected to the input of retriggerable multivibrator S6. Retriggerable multivibrator 56 remains in state Q until the pulses at its input are separated by more than a given time period which time period according to the invention is set to be equal to'the predetermined time period that it is desired to have switches 13 and 14 simultaneously opened for an output signal indication to be emitted. Output Q of retriggerable multivibrator 56 is connected to inverter 57 which provides an output indication representing a double feed when multivibrator 56 changes from state Q to state Q.

The output of NAND Gate 51 provides an input to AND Gate 55 at all times except when switches 13 and 14 are simultaneously open. The other input to AND Gate 55 is the source of clock pulses at the output of inverter. 54 which clock pulses are separated by less than the predetermined time period. Hence the output of AND Gate 55 supplies a train of clock pulses for a period less than the predetermined time period to the input of multivibrator 56 except when the pulses are gated off by no signal appearing at the output of inverter 51. This occurs only when the switches are simultaneously open and if the switches are simultaneously open for a time greater than the predetermined time period. Then multivibrator 56 will change to state Q, and inverter 57 will provide an output signal indicating a double feed. If desired, multivibrator 56 may be provided with a control for varying the predetermined time period.

In order to avoid the problem of paper dust generated by the documents being drawn into the switches where it may interfere with the operation thereof, fluid passageways 21 and 22 are coiled around themselves in a 360 degree are to prevent paper dust from reaching the switches. The fluid passageways of the system are periodically removed and cleaned to remove any paper dust which may have accumulated in them over a period of time.

FIG. 2 shows an alternate embodiment of one of the fluid loops of the detector of FIG. 1. In the embodiment of FIG. 2 instead of passageways 8 and 21 meeting at a junction where they are connected to passageway 39 which leads to port means 24 passageways 8 and 21, shown as passageways 45 and 48 in FIG. 2, are directly connected to each other at port means 46. Port means 46 is located in shoe 40 and includes passageways 41 and 48 which are connected to each other internally and connected to passageways 45 and 48 externally. The remainder of the loop shown in FIG. 2 is identical to the loop shown in FIG. 1.

While I have disclosed and described the preferred embodiments of my invention, I wish it understood that I do not intend to be restricted solely thereto, but that I do intend to include all embodiments thereof which would be apparent to one skilled in the art and which come within the spirit and scope of my invention.

I claim:

1. An apparatus for detecting the presence of overlapped planar members in a given area comprising a given area through which overlapped planar members may be passed, a normally open port means positioned on each side of said given area, each of said port means 'being connected in a different fluid circuit which is closed to the atmosphere except for the normally open port means, each of said fluid circuits comprising a continuous closed fluid loop when said members are against said port means, each of said fluid circuits further including a pressure responsive switch means and being connected to a vacuum source means whereby each of two overlapped planar members which may be present in said given area is attracted by the suction pressure of said vacuum source means against a different port means thereby closing both of said fluid circuits to the atmosphere and causing said pressure responsive switch means in each of said fluid circuits to change state, means connected to said switch means for indicating that both of said switch means are in said changed state simultaneously, each of said continuous fluid loops being connected to said vacuum source means by a fluid passageway which joins the loop at a junction where it connects with the ends of two portions of the loop, said portions being connected to each other at the other ends thereof, said switch means being located in one of said portions, said switch means being in a closed state when said port means are open due to the differential pressure across said switch means and said switch means being caused to change state when said planar members are against said port means due to a reduction in said differential pressure, there being a looped segment of fluid passageway in the part of said one of said portions of said fluid loops between said port means and said pressure responsive switch means for preventing foreign matter from reaching said switch means.

2. An apparatus for detecting the presence of overlapped planar members in a given area comprising a given area through which overlapped planar members may be passed, a normally open port means positioned on each side of said given area, each of said port means being connected in a different fluid circuit which is closed to the atmosphere except for the normally open port means, each of said fluid circuits comprising a continuous closed fluid loop when said members are against said port means, each of said fluid circuits further including a pressure responsive switch means and being connected to a vacuum source means whereby each of two overlapped planar members which may be present in said given area is attracted by the suction pressure of said vacuum source means against a different port means thereby closing both of said fluid circuits to the atmosphere and causing said pressure responsive switch means in each of said fluid circuits to change state, means connected to said switch means for indicating that both of said switch means are in said changed state simultaneously, each of said continuous fluid loops being connected to a vacuum source by a fluid passageway which joins the loop at a junction where it connects with the ends of two portions of the loop, said portions being connected to each other at the other ends thereof, said switch means being located in one of said portions, said switch means being in a closed state when said port means are open due to the differential pressure across said switch means and said switch means being caused to change state when said planar members are against said port means due to a reduction in said differential pressure, said means for indicating that both of said switch means are in said changed state simultaneously including means which provides an output indication only when said switch means are in said changed state simultaneously for a predetermined minimum period of time.

3. An apparatus according to claim 2 wherein said means which provides an output indication only when said switch means are in said changed state simultaneously for a predetermined minimum period of time includes means for providing an output signal and means for inhibiting the production of said output signal except when said switch means are simultaneously in said changed state for said predetermined minimum period of time.

4. An apparatus according to claim 3 wherein said means for inhibiting comprises two-state means arranged to change state only when the signals at its input are separated by a time greater than said predetermined minimum period of time.

5. An apparatus according to claim 4 further including means for generating an input pulse train for said two-state means successive pulses of which are separated by a time less than said predetermined minimum period of time, means for signalling when said switch means are in said changed state simultaneously and means for inhibiting said input pulse train from being applied to the input of said two-state means when said means for signalling means indicates that said switch means are in said changed state simultaneously.

6. An apparatus according to claim 5 wherein said two-state means comprises retriggerable multivibrator means.

7. An apparatus according to claim 6 wherein said means for inhibiting said input pulse train and said means for signalling include an AND gate.

8. A method for detecting overlapped documents passing through a given area comprising the steps of;

providing a pair of continuous, fluid flow loops which are closed to the atmosphere except for a normally open port means, locating said normally open port means on either side of said given area, providing a pressure responsive switch means in each of said flow loops, applying suction pressure to each of said flow loops, passing documents through said given area whereby if overlapped documents are present, each document will be attracted against a different port means by said suction pressure thereby completely closing said flow loops and causing said pressure responsive switch means to change state, providing an output indication when said pressure responsive switch means are in said changed state simultaneously, defining a minimum predetermined period of time, measuring the length of time that said switch means are simultaneously in said changed state, inhibiting said output indication unless said length of time exceeds said minimum predetermined period of time.

l I! II 

1. An apparatus for detecting the presence of overlapped planar members in a given area comprising a given area through which overlapped planar members may be passed, a normally open port means positioned on each side of said given area, each of said port means being connected in a different fluid circuit which is closed to the atmosphere except for the normally open port means, each of said fluid circuits comprising a continuous closed fluid loop when said members are against said port means, each of said fluid circuits further including a pressure responsive switch means and being connected to a vacuum source means whereby each of two overlapped planar members which may be present in said given area is attracted by the suction pressure of said vacuum source means against a different port means thereby closing both of said fluid circuits to the atmosphere and causing said pressure responsive switch means in each of said fluid circuits to change state, means connected to said switch means for indicating that both of said switch means are in said changed state simultaneously, each of said continuous fluid loops being connected to said vacuum source means by a fluid passageway which joins the loop at a junction where it connects with the ends of two portions of the loop, said portions being connected to each other at the other ends thereof, said switch means being located in one of said portions, said switch means being in a closed state when said port means are open due to the differential pressure across said switch means and said switch means being caused to change state when said planar members are against said port means due to a reduction in said differential pressure, there being a looped segment of fluid passageway in the part of said one of said portions of said fluid loops between said port means and said pressure responsive switch means for preventing foreign matter from reaching said switch means.
 2. An apparatus for detecting the presence of overlapped planar members in a given area comprising a given area through which overlapped planar members may be passed, a normally open port means positioned on each side of said given area, each of said port means being connected in a different fluid circuit which is closed to the atmosphere except for the normally open port means, each of said fluid circuits comprising a continuous closed fluid loop when said members are against said port means, each of said fluid circuits further including a pressure responsive switch means and being connected to a vacuum source means whereby each of two overlapped planar members which may be present in said given area is attracted by the suction pressure of said vacuum source means against a different port means thereby closing both of said fluid circuits to the atmosphere and causing said pressure responsive switch means in each of said fluid circuits to change state, means connected to said switch means for indicating that both of said switch means are in said changed state simultaneously, each of said continuous fluid Loops being connected to a vacuum source by a fluid passageway which joins the loop at a junction where it connects with the ends of two portions of the loop, said portions being connected to each other at the other ends thereof, said switch means being located in one of said portions, said switch means being in a closed state when said port means are open due to the differential pressure across said switch means and said switch means being caused to change state when said planar members are against said port means due to a reduction in said differential pressure, said means for indicating that both of said switch means are in said changed state simultaneously including means which provides an output indication only when said switch means are in said changed state simultaneously for a predetermined minimum period of time.
 3. An apparatus according to claim 2 wherein said means which provides an output indication only when said switch means are in said changed state simultaneously for a predetermined minimum period of time includes means for providing an output signal and means for inhibiting the production of said output signal except when said switch means are simultaneously in said changed state for said predetermined minimum period of time.
 4. An apparatus according to claim 3 wherein said means for inhibiting comprises two-state means arranged to change state only when the signals at its input are separated by a time greater than said predetermined minimum period of time.
 5. An apparatus according to claim 4 further including means for generating an input pulse train for said two-state means successive pulses of which are separated by a time less than said predetermined minimum period of time, means for signalling when said switch means are in said changed state simultaneously and means for inhibiting said input pulse train from being applied to the input of said two-state means when said means for signalling means indicates that said switch means are in said changed state simultaneously.
 6. An apparatus according to claim 5 wherein said two-state means comprises retriggerable multivibrator means.
 7. An apparatus according to claim 6 wherein said means for inhibiting said input pulse train and said means for signalling include an AND gate.
 8. A method for detecting overlapped documents passing through a given area comprising the steps of; providing a pair of continuous, fluid flow loops which are closed to the atmosphere except for a normally open port means, locating said normally open port means on either side of said given area, providing a pressure responsive switch means in each of said flow loops, applying suction pressure to each of said flow loops, passing documents through said given area whereby if overlapped documents are present, each document will be attracted against a different port means by said suction pressure thereby completely closing said flow loops and causing said pressure responsive switch means to change state, providing an output indication when said pressure responsive switch means are in said changed state simultaneously, defining a minimum predetermined period of time, measuring the length of time that said switch means are simultaneously in said changed state, inhibiting said output indication unless said length of time exceeds said minimum predetermined period of time. 